PHYCO-REMEDIATION OF AZO DYE CONTAMINATED WASTEWATER

Abstract

Synthetic dyes are widely used in textile, leather and other dye-stuff industries. A large fraction of the dyes applied during the dyeing processes are released into wastewater. Therefore, the wastewater from dye-related industries is very colorful, with high chemical oxidation and biological oxidation demand. This wastewater must be treated prior to discharge into wastewater streams to prevent pollution of surface and groundwater, and the risk to public health. The present study was designed with the aim to isolate potential strains of algae capable of degrading azo dyes for the treatment of textile wastewater. Eighty-eight algae strains were isolated on agar plates using modified MA medium. About 20 algal strains were screened by enrichment of the medium with 100 mg L-1 Reactive Blue azo dye. Out of 20 isolates of algae, two strains CKW1 (Spirogyra sp.) and PKS33 (Cladophora sp.) were able to decolorize 88% and 83% dye, respectively, in seven days incubation time. The substrate (dye) 100 mg L-1, pH 8, 30 °C temperature and 16 h light duration were found to be optimum conditions for maximum decolorization of azo dyes by these strains of algae. Under optimal conditions, both strains were able to completely decolorize the structurally different synthetic textile dyes and real textile wastewater in 96 h to 120 h. Algal cells showed a better efficacy in decolorizing real textile effluent than observed with dead algae biomass (dry). About 60% decolorization of the real textile wastewater was achieved by living cells in only 24 hours and 80% decolorization in 120 h. Toxicity analyses were performed in terms of hemolytic activity. The results showed that the treated wastewater with algae living biomass reduced the toxicity of wastewater by 70-80%, while a reduction of 30-35% of the toxicity was observed in the case of algae dead mass. The treated textile wastewater also improved significantly wheat growth compared to untreated real wastewater. Using the trans- esterification method, it was found that the algal biomass produced by the use of textile treated effluent could be used to produce biodiesel. These findings suggest that algae could be used to treat wastewater containing textile dyes that can be used for growing crop plants.